Sputtering target and method for preparation thereof

ABSTRACT

A sputtering target prepared by the butt joining of metal sheets being made of the same material, wherein an intermetallic compound in a joined portion has an average particle diameter of 60% to 130% of the average particle diameter of the intermetallic compound in a non-joined portion is provided. In the sputtering target, the average particle diameter of an intermetallic compound in a joined portion is approximately the same as that of the intermetallic compound in a non-joined portion.

TECHNICAL FIELD

The present invention relates to a sputtering target and a method forpreparation thereof, and in particular, to a large sputtering targetthat can be used in the production of large liquid crystal displays orthe like and a method for preparation thereof.

BACKGROUND ART

Recently, in order to increase the size of liquid crystal displays andto reduce the cost, liquid crystal panel manufacturers use a glasssubstrate having a dimension larger than 1 m square for the liquidcrystal displays. In the future, as the increase in the size of displaysadvances, a glass substrate having a dimension of about 2 m square willalso be used.

Wiring layers in a liquid crystal display are formed by sputtering. Inthe sputtering, a sputtering target (hereinafter also simply referred toas a target) having a dimension slightly larger than a glass substrateis generally used. For example, when a wiring layer is formed on a glasssubstrate having a dimension of about 1,100 mm×1,250 mm, a very largetarget having a dimension of about 1,431 mm×1,650 mm is used.

In general, sputtering must be satisfactorily performed without causingan abnormal discharge or the like, and in addition, a film having auniform composition, a uniform thickness, and the like must be formed bysputtering. In order to satisfy these requirements, a sputtering targetused must have a uniform composition, a uniform metallographicstructure, and the like.

The production of a sputtering target generally includes a method ofproducing a metallic material and a method of processing the resultantmetallic material to form a predetermined shape. Examples of the methodof producing a metallic material include melting and casting, powdermolding, and spray forming. Examples of the method of processing theresultant metallic material include hot isostatic pressing (HIP),forging, rolling, and machining and these methods are used incombination.

However, when a large sputtering target having a uniform composition andthe like is produced, the following problems occur: Apparatuses may belimited in the above-described production, or when the sputtering targetis produced with a large-scaled apparatus, a fine and uniformmetallographic structure or the like cannot be obtained.

For example, in a sputtering target containing an intermetallic compounddispersed in the metallographic structure, the intermetallic compound ispreferably dispersed finely and uniformly. When a metallic material isproduced by melting and casting, in general, quenching the moltenmetallic material is required so as to disperse an intermetalliccompound finely and uniformly. However, in producing a large target, asatisfactory quenching effect is difficult to be achieved because of anexcessive amount of the molten material. Therefore, it is difficult todisperse the intermetallic compound finely and uniformly. In addition,the manufacturing apparatus is limited in view of, for example, the sizeand the shape of an ingot.

When a metallic material is produced by powder molding or spray forming,a subsequent HIP treatment is required to densify the metallic material.However, in producing a large metallic material, the size of themetallic material to be formed is disadvantageously limited because ofthe restriction of an apparatus for HIP.

Hitherto, in a trial for producing a large target (thickness: about 6 toabout 20 mm), a method of welding two metal sheets with a welding rodhas been studied. Also, electron beam welding, laser welding, and thelike have been studied as welding methods that do not require a weldingrod.

However, in these methods, the entrapment of a welding gas or theentrapment of an oxide formed on the surface of a metal sheet causesdefects. In addition, the joined portion is melted and solidified, andconsequently, the structure of crystal grains is coarsened, comparedwith the non-molten portion. Therefore, the use of such a target causesa problem of arcing during sputtering. Furthermore, in the abovemethods, the crystal grains are coarsened and the crystal orientation isalso significantly changed at the same time. When such a target havingan uneven crystal orientation is used in sputtering, the sputtering rateis changed. Consequently, a stable film thickness cannot be obtained.

A method for joining metallic materials includes not only the abovewelding method but also a friction stir welding (FSW) method. Forexample, according to a document of “Behavior of oxide in joined portionduring friction stir welding of aluminum alloy and its influences onmechanical properties” (Yousetsu Gakkai Ronbunshu (Quarterly Journal ofthe Japan Welding Society), August 2001, Vol. 19, No. 3, pp. 446-456),by this FSW method, an aluminum alloy is joined by a frictional heatcaused by rotation between a rotating tool and a joining material andthe plastic flow at a temperature lower than the melting point. Also, inthe above document, from the viewpoint that an oxide film on the surfaceof the joining material is easily entrapped in the joined portion, atensile test, a bending fatigue test, and the like in the joined portionwere performed to investigate the effect of the oxide on the mechanicalproperties of the joined portion. The document describes the results ofthe mechanical properties.

According to a document of “FSW having an increasing number ofapplications” (Yousetsu Gijyutsu (Welding Technology), June 2002, pp.67-78), the friction stir welding method is applied in the fields ofships and marine structures, railroad vehicles, space aeronautics, andthe like, and high mechanical strength in a joined portion, which cannotbe achieved by the conventional welding methods, can be ensured.

In these documents, the improvement of mechanical properties in a joinedportion is investigated in order that a joined material is used asstructural elements in the fields of ships and marine structures,railroad vehicles, space aeronautics, and the like. However, thesestudies do not target a sputtering target with which a satisfactorysputtering can be performed without causing an abnormal discharge, and afilm having a uniform composition, thickness, and the like can beformed. Therefore, it is assumed that further studies are required inorder to apply the above friction stir welding method to the preparationof a sputtering target.

In view of the above situation, it is an object of the present inventionto provide a sputtering target prepared by the butt joining of metalsheets being made of the same material, wherein even when the target isapplied to a large sputtering target, the particle diameter and thedispersion state of metallic crystals or an intermetallic compound in ajoined portion are approximately the same as those in a non-joinedportion of the target.

DISCLOSURE OF INVENTION

The sputtering target according to the present invention that can solvethe above problems is prepared by the butt joining of metal sheets beingmade of the same material and has the following features (1) to (4).

(1) An intermetallic compound in a joined portion has an averageparticle diameter of 60% to 130% of the average particle diameter of theintermetallic compound in a non-joined portion.

(2) The average distance between adjacent intermetallic compoundparticles in a joined portion is 60% to 130% of the average distancebetween adjacent intermetallic compound particles in a non-joinedportion.

(3) The average of the grain diameter of metallic crystals in a joinedportion is 20% to 500% of the average of the grain diameter of metalliccrystals in a non-joined portion.

(4) No dendritic structure is generated in a joined portion.

Examples of the material of the sputtering target of the presentinvention include one element selected from the group consisting ofaluminum, an aluminum alloy, copper, a copper alloy, silver, and asilver alloy. When the sputtering target of the present invention isapplied to a target having a planar area of 1 m² or more, the advantagesof the present invention can be satisfactorily exhibited.

The present invention also specifies a method for preparation of asputtering target. The method includes a step of joining metallicmaterials being made of the same material by friction stir welding.During the joining, the moving distance of a rotating tool is preferably0.3 to 0.45 mm per revolution. Annealing is preferably performed afterthe joining. Furthermore, in the present invention, a metallic materialprepared by spray forming is preferably used because a sputtering targethaving a uniform composition and the like is easily produced. Thepresent invention also includes a sputtering target prepared by theabove method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing a friction stir weldingmethod performed in Examples.

FIG. 2 is a schematic cross-sectional view showing a rotating tool usedin Examples.

FIG. 3 is a cross-sectional view schematically showing the state of ajoining material (i.e., metal sheet) after joining.

BEST MODE FOR CARRYING OUT THE INVENTION

Under the above-described situation, the present inventors haveinvestigated the particle diameter and the dispersion state of metalliccrystals or an intermetallic compound in a joined portion and anon-joining portion of a sputtering target prepared by the butt joiningof metal sheets being made of the same material. The investigation hasbeen performed so that even when the target is applied to a largesputtering target, a satisfactory sputtering property is provided (forexample, an abnormal discharge does not occur) during sputtering, and inaddition, the resultant film has a uniform thickness and the like. As aresult, the present inventors have found that the following requirements(1) to (4) should be satisfied, and thus the present invention has beenmade.

(1) In a target containing an intermetallic compound dispersed in themetallographic structure, the intermetallic compound in a joined portionhas an average particle diameter of 60% to 130% of the average particlediameter of the intermetallic compound in a non-joined portion.

The reason for this is as follows. When the average particle diameter ofthe intermetallic compound in a joined portion exceeds 130% relative tothat of the intermetallic compound in a non-joined portion, a largeintermetallic compound is present in the joined portion, resulting in aproblem of, for example, increasing in the variation in the filmthickness during sputtering. The average particle diameter of theintermetallic compound in a joined portion is preferably 120% or less,more preferably, 110% or less of the average particle diameter of theintermetallic compound in a non-joined portion.

When the size of the intermetallic compound in a joined portion isexcessively smaller than that in a non-joined portion, the above problemoccurs. Accordingly, the average particle diameter of the intermetalliccompound in a joined portion is at least 60%, preferably at least 70%,and more preferably at least 80% of the average particle diameter of theintermetallic compound in a non-joined portion. In the most preferablecase, the average particle diameter of the intermetallic compound in ajoined portion is the same (100%) as the average particle diameter ofthe intermetallic compound in a non-joined portion.

(2) In a target containing an intermetallic compound dispersed in themetallographic structure, the average distance between adjacentintermetallic compound particles in a joined portion is 60% to 130% ofthe average distance between adjacent intermetallic compound particlesin a non-joined portion.

The reason for this is as follows. When the average distance betweenadjacent intermetallic compound particles in a joined portion exceeds130% relative to the average distance between adjacent intermetalliccompound particles in a non-joined portion, the intermetallic compoundparticles are sparsely dispersed. When a target having such a structureis used, the variation in the thickness of the resultant film is easilyincreased and a film having a uniform composition is not easilyobtained. The average distance between adjacent intermetallic compoundparticles in a joined portion is preferably 120% or less, morepreferably 110% or less, relative to the average distance betweenadjacent intermetallic compound particles in a non-joined portion.

When the average distance between adjacent intermetallic compoundparticles in a joined portion is excessively smaller than the averagedistance between adjacent intermetallic compound particles in anon-joined portion, the above problem occurs. Accordingly, the averagedistance between adjacent intermetallic compound particles in a joinedportion is at least 60%, preferably at least 70%, and more preferably atleast 75% of the average distance adjacent intermetallic compoundparticles in a non-joined portion. In the most preferable case, theaverage particle diameter of the intermetallic compound in a joinedportion is the same (100%) as the average particle diameter of theintermetallic compound in a non-joined portion.

(3) In a target that does not contain an intermetallic compound in themetallographic structure, the average of the grain diameter of metalliccrystals in a joined portion is 20% to 500% of the average of the graindiameter of metallic crystals in a non-joined portion.

The reason for this is as follows. When the average of the graindiameter of metallic crystals in a joined portion exceeds 500% of theaverage of the grain diameter of metallic crystals in a non-joinedportion, the metallic crystal grains in the joined portion aresignificantly coarsened, compared with those in the non-joined portion.When such a target is used in sputtering, the sputtering rate ischanged. Consequently, for example, a stable film thickness cannot beobtained. The average of the grain diameter of metallic crystals in ajoined portion is preferably 250% or less, more preferably 200% or less,of the average of the grain diameter of metallic crystals in anon-joined portion.

When the grain diameter of metallic crystals in a joined portion isexcessively smaller than the grain diameter of metallic crystals in anon-joined portion, the above problem occurs. Accordingly, the averageof the grain diameter of metallic crystals in a joined portion is atleast 20%, preferably at least 40%, and more preferably at least 50%relative to the average of the grain diameter of metallic crystals in anon-joined portion. In the most preferable case, the average of thegrain diameter of metallic crystals in a joined portion is the same(100%) as the average of the grain diameter of metallic crystals in anon-joined portion.

(4) Regardless of the presence or absence of an intermetallic compoundin the metallographic structure, no dendritic structure is generated ina joined portion.

In the butt joining of end faces of metal sheets by a known weldingmethod, a dendritic structure is easily generated when a joined portionis melted is then solidified. The use of a target having such astructure is not preferable because the thickness of the resultant filmis easily varied, and in addition, the composition of the film is notuniform.

For example, a sputtering target of the present invention is composed ofone element selected from the group consisting of aluminum, an aluminumalloy, copper, a copper alloy, silver, and a silver alloy. Examples ofthe aluminum alloy, the copper alloy, and the silver alloy includealloys of aluminum, copper, or silver each containing an element such asa transition metal element; a rare earth element, e.g., Nd; or Bi inorder to provide advantages such as heat resistance and corrosionresistance.

When the sputtering target of the present invention is used as a largetarget having a planar area of 1 m² or more, the advantages of thepresent invention can be satisfactorily exhibited. The shape of thetarget includes sheets having a planar area of a square, a rectangle, acircle, or an ellipse.

In order to produce a sputtering target prepared by the butt joining ofmetal sheets being made of the same material, wherein the particlediameter and the dispersion state of an intermetallic compound or thegrain diameter of metallic crystals in a joined portion is approximatelythe same as those in a non-joined portion, it is very effective to use afriction stir welding method in the joining. Unlike conventional weldingmethods, in the friction stir welding method, as described above, ajoined portion is not melted during joining and the plastic flow justoccurs at a temperature lower than the melting point. Therefore, thecoarsening of the metallic crystals in the joined portion is suppressed.Also, when an intermetallic compound is contained, the coarsening of theintermetallic compound is suppressed. Thus, a metallographic structurein the joined portion approximately the same as that in a non-joinedportion can be provided.

Specifically, for example, a friction stir welding is performed asfollows. As shown in FIG. 1, which will be described below, a rotatingtool 1 is screwed in a butted portion of materials 2 to be joined. Therotating tool 1 is composed of a material harder than that of thematerials 2 to be joined. The rotating tool 1 is moved on the buttedportion (i.e., joining line) of the materials 2 to be joined whilerotating, thus generating frictional heat. The frictional heat softens ametal disposed at the peripheral part of the rotating tool 1 to generatea plastic flow. Thus, the materials 2 are joined.

As a condition for the above friction stir welding, the moving distanceof the rotating tool used during joining is preferably 0.3 to 0.45 mmper revolution. When the moving distance per revolution of the rotatingtool is excessively short, in other words, when the travel speed of therotating tool is low and stirring at the same region becomes excessive,the temperature at the plastic flow region increases and a transformedstructure is generated outside of the region. On the other hand, whenthe moving distance per revolution of the rotating tool is long, inother words, when the travel speed of the rotating tool is high, anexcessive load is applied to the rotating tool and unevenness ofprocessing is generated.

When a tool having a shape shown in FIG. 2, which will be describedbelow, is used as the rotating tool, during joining, the rotating tool 1is preferably tilted by 3° to 5° relative to the plane of the materials(metal sheets) 2 to be joined so that a part of shoulder 6 is tilted inthe direction opposite to the traveling direction. In addition, theclearance between the materials 2 to be joined is preferably 0.03 mm orless during joining.

In the friction-stirred portion where a rotating tool has passed throughduring joining, the crystal orientation is changed because of theplastic flow. Therefore, a trace of stirring distinctly appears on thesurface after sputtering. Accordingly, in order to prepare a targethaving a flat face and a good appearance, the target is preferablyannealed so that the region that has been subjected to a highdeformation by the plastic flow is recrystallized. Thus, the extremechange in the crystal orientation in the plastic flowing region shouldbe reduced to remove the trace of stirring. From the viewpoint ofimproving the recrystallization and preventing the coarsening of crystalgrains, the annealing is preferably performed at, for example, 200° C.to 300° C. for a pure aluminum target, 250° C. to 500° C. for analuminum alloy target, 400° C. to 500° C. for a pure silver target, 450°C. to 700° C. for a silver alloy target, 400° C. to 550° C. for a purecopper target, and 450° C. to 750° C. for a copper alloy target. Inorder to completely remove the trace, the annealing time is preferablytwo hours or more. The annealing time is preferably 5 hours or lessbecause an excessively long annealing time coarsens the crystal grain.

The metallic material used in the production of a sputtering target ispreferably prepared by spray forming because the metallic material hasmore uniform composition or the like, compared with a metallic materialprepared by casting or powder molding. In an example of the above sprayforming method, a molten material is dropped from a nozzle having adiameter of a few millimeters, a gas such as N₂ gas is sprayed in themiddle of dropping so as to pulverize the material, and an intermediatematerial (density: about 50% to about 60%) called a preform is formedbefore the powdery material is completely solidified.

The present invention does not specify the conditions for otherproduction processes such as HIP, forging, and rolling, and theseprocesses may be performed under normal conditions. In an example of amethod for preparing a sputtering target, a metallic material preparedby the spray forming is densified with a HIP apparatus, and is thenforged to form a metallic material sheet. Furthermore, the sheet isrolled so that the thickness of the sheet is approximately the same asthat of the target to be formed. Subsequently, two metal sheets preparedby the same method are butted each other and are joined by friction stirwelding as described above. According to this method, even a largetarget having a uniform particle diameter and uniform dispersion stateof metallic crystals or an intermetallic compound can be preparedwithout limitation of apparatuses or the like.

EXAMPLES

The present invention will now be described more specifically along withexamples. The present invention is not limited to the followingexamples, and can be embodied with appropriate modifications so long asthe modifications fit the purposes described above and below. Thesemodifications are also included in the technical scope of the presentinvention.

EXAMPLE 1

[Preparation of Targets in Example (1) of the Present Invention]

An alloy material of Al-2 at % Nd was prepared by spray forming, and thealloy material was then densified by pressing at high temperature andhigh pressure. Subsequently, the resultant material was forged androlled to prepare metal sheets each having a dimension of 13.5 mm (inthickness)×730 mm×1,710 mm. Two metal sheets having the same dimensionwere prepared. As shown in FIG. 1, the sides of 1,710 mm were butted andjoined by friction stir welding.

The friction stir welding was performed as follows. Specifically, asshown in FIG. 2, a rotating tool 1 in which the diameter of a largediameter part 3 was 10 mm, the diameter of a small diameter part 4 was 8mm, a rotating tool length 5 was 12.5 mm, and the diameter of a shoulder6 was 20 mm was used in the joining.

During joining, the rotating tool 1 was tilted by 4° relative to theplane of materials (metal sheets) 2 to be joined so that the part of theshoulder 6 was tilted in the direction opposite to the travelingdirection. In this state, the rotating tool 1 was screwed in a buttedportion of the two materials (metal sheets) 2 to be joined. As shown inFIG. 1, the rotating tool 1 was moved on the butted portion of thematerials 2 to be joined while rotating.

The revolution speed of the rotating tool 1 was 1,000 rpm, and thetraveling speed of the rotating tool 1 was 400 mm/min (accordingly, themoving distance per revolution of the rotating tool 1 was 0.4 mm). Asshown in FIG. 3, the height of the rotating tool 1 was adjusted so thatthe depth of a plastic flow portion 7 was about 13 mm and the remainingportion, which was not joined, was about 0.5 mm in the thickness of thesheet of 13.5 mm.

The calculated dimension of the sheet after joining was 13.5 mm (inthickness)×1,460 mm×1,710 mm. However, a portion where the rotating tool1 was inserted (i.e., the initial portion of joining) and a portionwhere the rotating tool 1 was pulled out (i.e., the end portion ofjoining) could not be used as a product because these portions wereregions processed by excessive heat. Consequently, the effectivedimension of the metal sheet after joining was 13.5 mm (inthickness)×1,460 mm×about 1,680 mm.

Subsequently, the joined metal sheet was annealed in a heat-treatingfurnace at 450° C. for 2 hours. Another joined metal sheet that was notannealed was also prepared. In each of the metal sheets, 1 mm of thejoined surface and 2.5 mm of the other surface including the remainingportion, which was not joined, were ground. Thus, targets each having athickness of about 10 mm were prepared.

[Observation of Structure of Target in Example (1) of the PresentInvention]

The surface (of the joined side) of the resultant target (the annealedtarget) was observed with an electron microscope. In a non-joinedportion on the surface, 30 intermetallic compound particles wereobserved per field of view. Also, in a joined portion on the surface, 30intermetallic compound particles were observed per field of view. Theparticle diameters of intermetallic compound particles each having adiameter of at least 1 μm, and the nearest-neighbor distances betweenintermetallic compound particles each having a diameter of at least 1 μmwere measured to calculate each average. Table 1 shows the results.TABLE 1 Example (1) of the present invention Comparative Example (1)Non-joined portion Joined-portion Molten portion Distance DistanceDistance Diameter (μm) to the Diameter (μm) to the Diameter (μm) to the(μm) of nearest (μm) of nearest (μm) of nearest intermetallicintermetallic intermetallic intermetallic intermetallic intermetalliccompound compound compound compound compound compound No. particleparticle particle particle particle particle 1 1.75 10.25 1.25 1.25 93.981.8 2 2 3.75 1.5 1.25 21.2 51.5 3 1.25 4.25 1.25 8.5 61 24.2 4 1.756.25 1.5 5.25 12.1 21.2 5 1.25 5.75 1.5 5.25 139.4 30.3 6 2.25 5.75 1.51.75 21.2 30.3 7 1.5 5.75 1.25 1.75 21.2 45.5 8 1.5 2.75 1 4 24.2 30.3 91 5.75 1 1.75 66.7 30.3 10 1.5 1 1.5 1.75 9.1 18.2 11 1.25 1 1.25 3 15.218.2 12 1.25 1.75 1 3 24.2 33.3 13 1.75 1.75 1 1.75 15.2 30.3 14 1.254.75 1.5 1.75 30.3 24.2 15 1.5 4 1.75 2.75 24.2 33.3 16 1.5 4 1 1.5 51.524.2 17 1.25 1.5 1.75 1.5 27.3 15.2 18 1.5 1.5 1.25 2.75 30.3 15.2 191.5 4.75 1.5 4.5 24.2 18.2 20 1.5 4.5 1 1 21.2 30.3 21 1.5 4.5 1 1 15.233.3 22 1.5 5 1.25 2.75 18.2 30.3 23 1.5 2.25 1.5 2.75 24.2 27.3 24 1.251 1.25 3.25 15.2 27.3 25 1.25 8 1 3.25 45.5 27.3 26 1.5 3.25 1.25 11.2521.2 26.7 27 2 8.25 1.25 3.25 24.2 18.2 28 1.5 11.5 1.5 7.75 15.2 15.229 1.25 1.75 1 3 15.2 24.2 30 1.5 1.75 1 3.5 51.5 33.3 Average 1.5 4.31.3 3.3 32.6 29

As shown in Table 1, the average diameter of the intermetallic compoundparticles each having a diameter of at least 1 μm in the non-joinedportion was 1.5 μm, whereas that in the joined portion was 1.3 μm. Theaverage diameter of the intermetallic compound particles in the joinedportion was 87% of the average diameter of the intermetallic compoundparticles in the non-joined portion.

The average distance between intermetallic compound particles eachhaving a diameter of at least 1 μm in the non-joined portion was 4.3 μm,whereas that in the joined portion was 3.3 μm. The average distancebetween adjacent intermetallic compound particles in the joined portionwas 77% of the average distance between those in the non-joined portion.

These results showed that the average diameter of the intermetalliccompound particles and the average distance between intermetalliccompound particles in the joined portion were approximately the same asthose in the non-joined portion.

[Sputtering Experiment Using Targets in Example (1) of the PresentInvention]

Sputtering was performed using the above annealed target and the targetthat was not annealed, and the surfaces after sputtering were observed.The sputtering was performed with a DC magnetron sputtering apparatus.During sputtering, the pressure of argon gas was 2 mTorr, the power(electric power) density was 6.4 W/cm², and the distance between asubstrate and the target was 62 mm. Sputtering was performed under theseconditions for 3 hours, the surface of each target was then visuallyobserved. The result showed that, on the annealed target, the trace ofthe rotating tool was reduced, compared with the trace of the rotatingtool on the target that was not annealed.

In addition, in order to evaluate the sputtering stability, the count ofabnormal discharges was measured. As a result, the count of abnormaldischarges in this example was smaller than that in Comparative Example(1), which will be described below. Furthermore, in films formed withthe targets of the present invention, the variation in the filmthickness was within the range of the average±3%. Thus, films having anapproximately uniform thickness were formed.

[Preparation of Target in Comparative Example (1)]

A sputtering target was prepared as in Example 1 including annealingexcept that the joining was performed by electron beam (EB) welding. Inthe EB welding, the degree of vacuum was 1×10⁻⁴ Torr, a negativeelectrode having a diameter of 4 mm was used, the accelerating voltagewas 60 kV, the beam current was 75 mA, and the welding speed was 400mm/min.

[Observation of Structure of Target in Comparative Example (1)]

The surface (of the joined side) of the sputtering target (the annealedtarget) prepared by joining by electron beam welding was observed withan electron microscope as in Example (1) of the present invention. Theaverage of particle diameters of intermetallic compound particles eachhaving a diameter of at least 1 μm and the average of nearest-neighbordistances between intermetallic compound particles each having adiameter of at least 1 μm were calculated. Table 1 includes the results.

Referring to Table 1, the average diameter of the intermetallic compoundparticles each having a diameter of at least 1 μm in the non-joinedportion was 1.5 μm, whereas that in a joined portion (i.e., moltenportion) was 32.6 μm. The average diameter of the intermetallic compoundparticles in the joined portion (molten portion) exceeded 20 times(2,000%) of the average diameter of intermetallic compound particles inthe non-joined portion. This result showed that the coarseningsignificantly proceeded.

The average distance between intermetallic compound particles eachhaving a diameter of at least 1 μm in the non-joined portion was 4.3 μm,whereas that in the joined portion (molten portion) was 29 μm. Theaverage distance between adjacent intermetallic compound particles inthe joined portion (molten portion) was 674% of the average distancebetween those in the non-joined portion. Thus, the intermetalliccompound particles were significantly sparsely dispersed. In addition,it was confirmed that a part of the structure in the joined portion(molten portion) was a dendritic structure.

[Sputtering Experiment Using Target in Comparative Example (1)]

In order to evaluate the sputtering stability, the count of abnormaldischarges was measured. In the same integral discharging powerconsumption as that in Example (1) of the present invention, the countof abnormal discharges was larger than that in Example (1) of thepresent invention. The possible reason was that the surface of thetarget in Comparative Example (1) had large irregularities because ofthe coarsening of the intermetallic compound.

In a film formed with the target in Comparative Example (1), thevariation in the film thickness was represented by the average +5%,which was larger than that in Example (1) of the present invention.

EXAMPLE 2

[Preparation of Targets in Example (2) of the Present Invention]

Next, targets were prepared using a material in which an intermetalliccompound was not precipitated. In this experiment, an alloy material ofAg-1 at % Bi-0.9 at % Cu was prepared by melting and casting. Theresultant material was forged and rolled to prepare metal sheets forjoining each having a dimension of 11 mm (in thickness)×650 mm×1,180 mm.As in FIG. 1, the sides of 1,180 mm of the two metal sheets were buttedand joined by friction stir welding under the same conditions as thosein Example 1.

The calculated dimension of the sheet after joining was 13.5 mm (inthickness)×1,180 mm×1,300 mm. However, a portion where the rotating tool1 was inserted (i.e., the initial portion of joining) and a portionwhere the rotating tool 1 was pulled out (i.e., the end portion ofjoining) could not be used as a product. Consequently, the effectivedimension of the metal sheet after joining was 13.5 mm (inthickness)×1,180 mm×about 1,270 mm.

Subsequently, the joined metal sheet was annealed in a heat-treatingfurnace at 450° C. for 2 hours. Another joined metal sheet that was notannealed was also prepared. In each of the metal sheets, 1 mm of thejoined surface and 2.5 mm of the other surface including the remainingportion, which was not joined, were ground. Thus, targets having athickness of about 10 mm were prepared.

[Observation of Structure of Target in Example (2) of the PresentInvention]

The surface (of the joined side) of the resultant target (the annealedtarget) was observed with an electron microscope. The length of majoraxis and the length of minor axis of metallic crystals were measured. Ina non-joined portion on the surface, 30 metallic crystals were measured.Also, in a joined portion on the surface, 30 metallic crystals weremeasured. The average calculated from the length of major axis and thelength of minor axis was defined as a crystal grain diameter. Table 2shows the results. TABLE 2 Example (2) of the Comparative presentinvention Example (2) Non-joined portion Joined-portion Molten portionCrystal grain Crystal grain Crystal grain No. diameter (μm) diameter(μm) diameter (μm) 1 31.6 135 925 2 50 140 1,295 3 48.7 65.6 1,203 463.1 124 879 5 36.8 141 463 6 55.2 57 1,249 7 43.4 113 786 8 68.4 1101,008 9 52.6 91.2 749 10 42.1 102 867 11 73.6 104 348 12 50 71.3 888 1351.3 89.8 1,036 14 65.8 162 1,129 15 52.6 102 944 16 73.6 107 1,055 1744.7 150 759 18 57.9 74.8 490 19 50 77 592 20 23.7 110 833 21 34.2 75.51,064 22 21 147 842 23 36.8 152 666 24 44.7 81.2 676 25 55.2 117 574 2627.6 101 786 27 35.5 145 944 28 26.3 72.8 916 29 44.7 69.8 1,101 30 27.6123 638 Average 46.3 107 856.8

As shown in Table 2, the average of the grain diameter of metalliccrystals in the non-joined portion was 46.3 μm, whereas that in thejoined portion was 107 μm. Accordingly, the average of the graindiameter of metallic crystals in the joined portion was 231% of theaverage of that in the non-joined portion. This result showed that thecoarsening was suppressed, compared with that in Comparative Example(2), which will be described below.

[Sputtering Experiment Using Target in Example (2) of the PresentInvention]

In order to evaluate the sputtering stability, the count of abnormaldischarges was measured. In the same integral discharging powerconsumption as that in the following Comparative Example (2), the countof abnormal discharges was smaller than that in Comparative Example (2).Furthermore, when sputtering was performed with the target of thepresent invention, the variation in the film thickness was representedby the average +5%. A film having more uniform thickness was obtained,compared with a film in the following Comparative Example (2).

[Preparation of Target in Comparative Example (2)]

A sputtering target was prepared as in Example (2) of the presentinvention except that the joining was performed by electron beam (EB)welding. The EB welding was performed under the same conditions as thosein Comparative Example (1).

[Observation of Structure of Target in Comparative Example (2)]

The surface (of the joined side) of the resultant sputtering target (theannealed target) was observed with an electron microscope as in Example(2) of the present invention. The length of major axis and the length ofminor axis of each metallic crystal were measured, and the averagethereof was defined as a crystal grain diameter. Table 2 includes theresults.

Referring to Table 2, the average of the grain diameter of metalliccrystals in the non-joined portion was 46.3 μm, whereas that in a joinedportion (molten portion) was 857 μm. The average of the grain diameterof metallic crystals in the joined portion (molten portion) was about 20times (1,851%) of the average of that in the non-joined portion. Thisresult showed that the coarsening significantly proceeded.

[Sputtering Experiment Using Target in Comparative Example (2)]

In order to evaluate the sputtering stability, the count of abnormaldischarges was measured. In the same integral discharging powerconsumption as that in Example (2) of the present invention, the countof abnormal discharges was larger than that in Example (2) of thepresent invention. The possible reason was that the surface of thetarget in Comparative Example (2) had large irregularities because ofthe coarsening of crystal grains. As a result, the abnormal dischargeswere increased.

In a film formed with the target in Comparative Example (2), thevariation in the film thickness was represented by the average ±10%,which was larger than that in Example (2) of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is constituted as described above and can providea sputtering target prepared by the butt joining of metal sheets beingmade of the same material. Even when the target is applied to a largesputtering target, the particle diameter and the dispersion state ofmetallic crystals or an intermetallic compound in a joined portion areapproximately the same as those in a non-joined portion of the target.

The realization of this large sputtering target having a uniformstructure allows large liquid crystal displays with high performance tobe produced.

1. A sputtering target prepared by the butt joining of metal sheetsbeing made of the same material, wherein an intermetallic compound in ajoined portion has an average particle diameter of 60% to 130% of theaverage particle diameter of the intermetallic compound in a non-joinedportion.
 2. A sputtering target prepared by the butt joining of metalsheets being made of the same material, wherein the average distancebetween adjacent intermetallic compound particles in a joined portion is60% to 130% of the average distance between adjacent intermetalliccompound particles in a non-joined portion.
 3. A sputtering targetprepared by the butt joining of metal sheets being made of the samematerial, wherein the average of the grain diameter of metallic crystalsin a joined portion is 20% to 500% of the average of the grain diameterof metallic crystals in a non-joined portion.
 4. A sputtering targetprepared by the butt joining of metal sheets being made of the samematerial, wherein no dendritic structure is generated in a joinedportion.
 5. The sputtering target according to claim 1, comprising oneelement selected from the group consisting of aluminum, an aluminumalloy, copper, a copper alloy, silver, and a silver alloy.
 6. Thesputtering target according to claim 1, comprising a planar area of 1 m²or more.
 7. A method for preparation of a sputtering target comprising astep of joining metallic materials being made of the same material byfriction stir welding.
 8. The method for preparation of a sputteringtarget according to claim 7, wherein the moving distance of a rotatingtool is 0.3 to 0.45 mm per revolution to perform the joining.
 9. Themethod for preparation of a sputtering target according to claim 7,wherein annealing is performed after the joining.
 10. The method forpreparation of a sputtering target according to claim 7, wherein ametallic material prepared by spray forming is used.
 11. A sputteringtarget prepared by the method according to claim
 7. 12. The sputteringtarget according to claim 2, comprising one element selected from thegroup consisting of aluminum, an aluminum alloy, copper, a copper alloy,silver, and a silver alloy.
 13. The sputtering target according to claim3, comprising one element selected from the group consisting ofaluminum, an aluminum alloy, copper, a copper alloy, silver, and asilver alloy.
 14. The sputtering target according to claim 4, comprisingone element selected from the group consisting of aluminum, an aluminumalloy, copper, a copper alloy, silver, and a silver alloy.
 15. Thesputtering target according to claim 2, comprising a planar area of 1 m²or more.
 16. The sputtering target according to claim 3, comprising aplanar area of 1 m² or more.
 17. The sputtering target according toclaim 3, comprising a planar area of 1 m² or more.
 18. A sputteringtarget prepared by the method according to claim
 8. 19. A sputteringtarget prepared by the method according to claim
 9. 20. A sputteringtarget prepared by the method according to claim 10.